Chloroquine is still the antimalarial drug which is the most utilized. Nevertheless the molecular mode of action of this drug is not very well understood. When mouse erythrocytes injected with Plasmodium berghei are exposed to chloroquine, the first biochemical event is rapid accumulation of the drug. This process is energy dependent, saturable and competively inhibited by drugs of the same therapeutic class (Quinine, Amodiaquine, Mefloquine). Receptors for chloroquine have been proposed for the process of accumulation. The nature of the chloroquine receptor is presently the subject of debates. The latest hypothesis proposed by Chou and coll. [12], is that ferriprotoporphyrin IX, formed by the degradation of hemoglobin by the parasite, binds to chloroquine with a dissociation constant of 3.5.10−9 M. We studied here the molecular interactions between these two species by Proton Nuclear Magnetic Resonance in order to elucidate the nature and the geometry of were undertaken.The perturbations of the NMR spectra of chloroquine (10−2 M) induced by addition of hematin or hemin were measured. Two types of measures were indertaken.The first study carried out in organic solvent (DMSO) has shown that the interaction occured between the acidic functions of hemin and the sidechain nitrogen of chloroquine. The iron atom was not implicated in this process.The second study carried out in aqueous medium (phosphate buffer; 0.1 M; pH = 7) allowed us to demonstrate that chloroquine is able to intercalate into a polymer of hematin. The quinoleic nucleus of chloroquine was intercalated between two dimers of hematin as shown by the broadening of the signal of the quinoleic protons due to very large increase in the correlation time.Finally it was shown that chloroquine is associated as a dimer in aqueous medium by hydrophobic interactions. The association constant is 5.5 M−1. 相似文献
Polarographic study of the mobilization of ferritin ironPolarographic study allows to propose a model for mobilization of ferritin iron: an equilibrium exists between iron core and small quantities of iron outside the protein.These iron atoms would be lying on electron acceptor sites including SH groups. The number of sites is dependent on iron content of ferritin.Therefore, the iron could be removed by the action of reducing agents such as xanthine oxidase or ascorbic acid, and then chelated by a complexing agent. 相似文献
Helix–coil transition of poly(γ-methyl-L -glutamate), poly(γ-ethyl-L -glutamate), and poly(γ-benzyl-L -glutamate) has been studied in mixed solvents by calorimetry, polarimetry, and viscometry. The experimental data have allowed the evaluation of solvation enthalpy Δhb, equilibrium constant K for hydrogen bond formation between the active solvent component and CO and NH groups, and the cooperativity parameter σ. The conformational transition of polypeptides in solution in a mixed solvent containing enough active solvent to maintain the coiled conformation has been produced by dilution with the helix-supporting solvent for the measurements of enthalpy of transition Δhs. The average value for Δhs is 3550 ± 300 J/mol and is practically independent of the nature of the side chain for the dichloroacetic acid-ethylene dichloride solvent pair at 25°C. A noticeable concentration effect exists in the case of poly(γ-benzyl-L -glutamate). The helical conformation is less stable for poly(γ-ethyl-L -glutamate), and this is explained by a steric effect hindering the access of dichloroacetic acid to side chains. Constant K has been calculated using polarimetric data and also from values of Δhs obtained at different temperatures using the Bixon and Lifson theory on the one hand and that of Sayama and coworkers on the other hand. Values of σ for poly(γ-ethyl-L -glutamate) have been calculated according to both theories mentioned, and the results show that the two sets of values are quite similar. The constant σ depends on the nature of the active solvent, on temperature, and on the binary-solvent composition. These conclusions are confirmed by viscometric results. Values of Δhb calculated from constant K are 5230 J/mol when Bixon and Lifson theory is used and 5569 J/mol when the theory at Sayama and coworkers is used. In both cases the value for Δhb is much lower than that of an intramolecular hydrogen bond. Experimental results suggest that the solvation mechanism would proceed in a manner so that mechanisms described in both theories are involved. 相似文献
Physicochemical studies of calf thymus chromatin were performed on micromicellar suspensions by thermal denaturation. These diluted suspensions were obtained, by a controlled shearing method, from a compact gel chromatin. Sedimentation and free-flow electrophoresis determined the size distribution of these particles. The most important result is a new transition on the melting profiles corresponding to a sudden increase of solution turbidity. This chromatin solution transition occurs at a higher temperature than usual DNA transition. The degree of « turbidity transitiondiminishes with micelle size but disappears when they are very mildly degraded by DNAases and when F1 histone fraction is removed.This transition is not only size dependent but also depends on the micellar structure. This phenomenon is interpreted as an excluded volume effect by contact between compact and native regions of nucleoprotein micelles and denatured coils of DNA. Our study tried to show that the degree of turbidity transition can be a criterion of chromatin native structure. 相似文献
Two classes of low-affinity Ca2+-binding sites have been shown to exist. One type dissociates as pH rises, thereby increasing the amount of bound Ca2+. The other type, which does not change in number, has an affinity for Ca2+ which is dependent on ionic strength. The former is possibly a phospholipid, the latter possibly a protein.Under our experimental conditions, the inner mitochondrial membrane contained binding sites of the second class ony while other membranes contain both types. Rough endoplasmic reticulum contains yet another class of sites at the ribosomal level.
Résumé
L'existence de deux catégories de sites de fixation de faible affinité du Ca2+ a été mise en évidence. Les uns se dissocient de plus en plus quant le pH s'éléve permettant une augmentation des quantités de Ca2+ fixé, les autres sont invariables en nombre, mais leur affinité pour le Ca2+ est dépendante de la force ionique du milieu. Les premiers pourraient étre de nature phospholipidique, les seconds de nature protéique.Dans nos conditions expérimentales, la membrane interne des mitochondries possède uniquement des sites de la seconde catégorie. Les autres membranes renferment simultanément les deux sortes de sites. Le réticulum endoplasmique rugueux possède des sites supplémentaires au niveau des ribosomes. 相似文献
The various polymer–acid solvation possibilities occuring in the helix–coil transition process of polypeptides with polar side chains were systematically analyzed by infrared spectroscopy. The following samples have been considered: poly-γ-benzyl-L -glutamate (PBLG), alternating poly-γ-benzyl-D ,L -glutamate (PBD-LG), and poly-β-benzyl-L -as-partate (PBLA). The behavior of the amide A, I, II, and νC?O ester absorptions of each polymer dissolved in trifluoroacetic acid–chloroform mixtures was studied in depth. The classical assumptions concerning the interaction between a polypeptide and a proton donor solvent are discussed. This interaction was previously proposed in a theoretical model of helix–coil transition. For PBLG, the spectral characteristics of the cooperative transition are evidenced by the amide bands. These bands also show main chain–acid hydrogen bonding (I) Quantitative analysis of phenomenon (I) was performed in order to localize the “binding sites” of the polymer. In agreement with the theory, only the complexation of peptide units belonging to random coil and terminal helical regions were observed. However, in contrast to the theory in which the association constants KCO and KNH of these residues are generally kept equal, the present results have shown that the main binding site is the carbonyl group (KNH ? 0 or « KCO ). The behavior of the polar side chains of these polypeptides were analyzed during the transition. Similarly to the peptide backbone, they bind the acid by hydrogen bonding (II) Furthermore, this association is more important when the side chains are localized in the coiled regions than in the helical ones. This result suggests, by analogy with the main chain behavior, that the helix–coil transition theory should take into account two more association constants for polar side chains, namely k1 for the helical regions and k2 > k1 for the coiled ones. 相似文献
D-glucose specifically deuterated at C-6 was prepared and used for the biosynthesis of bacterial cellulose with Acetobacter xylinum. The material obtained was converted into glucitol hexaacetate and analyzed by 250 MHz n.m.r. and mass spectrometry. These spectra indicated that about 70% of the starting D-glucose was incorporated without modification of deuteriation at the C-6 position. However an explanation is required of the finding that deuterium was also incorporated at the C-2 and C-1 positions of the cellulose, arising respectively from the 6 pro-R and 6 pro-S positions of the initial D-glucose. 相似文献
A comparative study of the sexual sequence is carried out in four Oniscoidea of the ligiid series Porcellio laevis, Metoponorthus sexfasciatus (Porcellionidae), Armadillidium vulgare (Armadillidiidae) and Armadillo officinalis (Armadillidae). The differences between the four species chiefly appear in the precopulatory manoeuvres. The integration of coiling or uncoiling reactions in the sexual sequence of coiling forms is studied in two genera: Armadillidium and Armadillo. Results of the behavioral study provide information about the evolution of the group. 相似文献
Commercial aqueous 25 per cent glutaraldehyde solutions contain no stable derivative of this aldehyde, but compounds of variable molecular weight which easily revert to glutaraldehyde. The effect of pH on the reaction of glutaraldehyde with amino acids and on the stability of the products under acid conditions, shows the importance of the structure modification of the dialdehyde which occurs when pH increases, and even leads to precipitation in highly alkaline solutions. This precipitate results from aldol condensation of glutaraldehyde molecules. It contains aldehyd groups conjugated with ethylenic double bonds. Such a structure reacts with amino groups to give an imino bond, stabilized by resonance with the ethylenic bond, and does not undergo Michael-type addition reactions.Therefore, glutaraldehyde does not react with proteins under its free form, but as an unsaturated polymer, which gives imino bonds stabilized by conjugation. 相似文献
Forty-seven navigation buoys were used to collect quantitative samples of epibenthic fauna in the Lower Estuary and Gulf of St. Lawrence. Stations, as described by their sessile species and biomass composition, were grouped using multivariate analysis. A Gower similarity index, modified to take into account the importance of each species in the ecosystem, was used to compare stations. Results obtained by cluster and principal coordinate analyses showed comparable relations between stations. North Shore and Gaspé Coast stations were separated from those of the Lower North Shore, the Mingan Island sector and the Lower Estuary. Stations from the Lower North Shore were also separated from those of the Mingan Island region and of the Lower Estuary, but at a higher level of similarity. All animal assemblages consisted of the following sessile species: Obelia longissima (Pallas), Hiatella arctica (L.), Mytilus edulis L., Balanus balanoides (L.) and B. crenatus (Bruguière). These species formed over 95% of biomass of all sessile species. Differences between the various station assemblages were mainly due to changes in the relative abundance of these species. The geographical gradient of summer surface water temperature best explains the observed clusters. In the Lower Estuary, the spatio-temporal variations of physico-chemical factors and the surface circulation may influence the number of species and their abundance. The circulation systems of the Lower Estuary and near the Mingan Islands might account for the similarity between their assemblages. The same dominant species, Obelia longissima, characterizes the fauna of these two regions. 相似文献
Proton magnetic resonance spectra of model dipeptide molecules R1–C′1O1–N2H2–CHR2–C′2O2–N3H3–R3 in CCl4 solutions exhibit splited signals when investigating on mixtures of L and D enantiomers differing from the racemic composition. The major effect is observed on amide proton signals which are the ones most sensitive to the ratio of aggregation. The stereoselective dimerization of enantiomeric molecules in the so-called C5 conformational state is shown to be responsible for such a phenomenon, the intensity of which depends on the bulkiness of the side chain R2. A theoretical approach is proposed which gives predictions in close agreement with our own experimental findings. 相似文献
This article firstly summarizes the process of study of an old collection, which had not been considered since the excavations at the site Les Vachons, started before 1914 and completed around 1939. The studied collection of J. Coiffard, both excavator and inventor of this site, includes four-fifths of the artefacts because, in 1940, he donated approximately one fifth to the Eyzies Museum. For his part, J. Bouyssonie who participated in the excavations for 3 years gave the major part of his own collection to the Archaeological Society of Charentes Angouleme where its condition makes it difficult to analyze. Despite these restrictions, based on statistical comparisons with counts many other sites, I came to the conclusion that the top three layers of Les Vachons are a confirmation of the Gravettian model, developed by B. Bosselin and F. Djindjian through their factor analysis. This model seems much better suited to the stratigraphy of Les Vachons, than all assumptions made by previous analysts in their attempt to bring the industries from the three layers in what remains from the Peyrony model. 相似文献